In many applications, visible or invisible reference lines are projected which serve, either for the human eye or for electronic systems, as a reference which also permits automatic positioning or machine guidance. Here, the reference lines are generally produced by divergence of a laser beam, which is possible in particular for straight lines, or by projection of a laser spot which is moved along a trajectory, which in principle permits any desired paths and hence reference lines.
Rotary lasers, which serve for establishing a plane with a visible or invisible laser beam and have been in use for many years, for example in the construction sector or in industry, are an example of this. They are a valuable aid for marking construction lines along horizontal, vertical or defined skew planes. However, rotary lasers to date have the disadvantage of defining only one dimension, such as height or skewness, which reduces the efficiency for the user.
Other systems are, for example, laser levels having a nadir or zenith beam, which are suitable for defining plumb lines for walls, riser pipes, cable ducts, air-conditioning shafts, horizontal windowsills, installation panels, pipes and cables. These reference lines may be detectable to the eye or to an optical detector, in general a mark visible to the eye being produced.
A laser level projects only a line on the irradiated object, as a rule in conjunction with a defined height to be specified visibly to the user. The information used here was therefore likewise only one dimensional. Often, however, it is also intended to determine or visualize even further information, for example there is for certain tasks the need to measure, to check or to obtain in visible form not only the height but also the distance (x) of the lateral position (x, y) from a point, for example in the case of renovation of a flat roof, where the sags must be known not only in height but also in lateral position. Moreover, no information about the surface onto which a projection takes place is available to systems to date for projecting reference lines. Without a knowledge of shape and position of the surface relative to the system, a projection can lead to distortion of the projected reference lines.
Furthermore, a lack of knowledge of the surface makes marking adapted to said surface completely impossible. If, for example, holes are to be drilled at a defined distance to the left and right of a door opening, it has been necessary to date to carry out a separate measurement manually, by means of which the lateral distance is determined. A projected reference line serves only for specifying the height of these drilled holes. In particular, systems of the prior art cannot automatically identify such a structure.
Systems generally known from the prior art for determining dimensions are laser scanners which scan and survey the surfaces point-by-point along a measuring path. However, they do not provide any functionalities which can specify a reference line or project a visible mark which in turn would permit an interaction with the user. There is therefore no linkage of surface determination and output of detectable or perceptible information or markings. Moreover, owing to their intended use, scanners have only a precision of the measurements relative to one another, and high-precision specification of a direction (orientation) relative to an external or global coordinate system is accordingly neither required nor realized by the apparatus, so that vertical plumbing with such apparatuses is too inaccurate. Moreover, precise vertical measurement which meets the requirements or specifications in the building sector is not possible.
A combination of distance-measuring and projection functionality is disclosed in US 2007/0044331 A1, in which a laser level with an ultrasonic distance-measuring unit is disclosed. The static leveller produces two laser fans arranged orthogonally in a cross. The US rangefinder is positioned next to the common axis of these two fans and measures in this direction the polar distance to the target object, the laser apparatuses themselves being suspended from a pendulum. The two laser fans are thus oriented relative to the perpendicular. The rangefinder on the other hand is fastened to the housing and points exactly in the direction of the line of intersection of the two laser fans only in the case of levelling of the instrument. In other dispositions, the surveyed target point is not known accurately. The manner of the distance measurement is therefore not linked to the levelling function, the two functions also not being integrated by the device. In the case of distance measurements, the device is used as an independent, hand-held distance tool. Thus, for example in the case of volume measurement, the user must reposition the device three times and carry out corresponding distance measurements in each case in three independent dispositions oriented as far as possible at right angles to one another. A levelling function or a direction measurement is not utilized.
Ultrasonic rangefinders moreover have accuracies in the cm range and are therefore too inaccurate for most construction requirements. Particularly disadvantageous is the sound wave which is caused to diverge by diffraction and assumes a dimension of several cm at the target object. Edges of girders or door frames cannot be surveyed therewith.
US 2006/0044570 A1 discloses a laser-based position determination device. It comprises at least one laser emitter having a rotation in a horizontal plane with a synchronization signal relative to a reference angle based on this axis. If the transmitted beam strikes a detector, which is positioned in each case at the target point to be surveyed, it acts as a position-sensitive photosensor by means of which the pulse length as a function of time and the phase angle can be determined. From phase position and pulse length, angular position and radial distance to the detector can then be determined. The apparatus can be used for 2D and for 3D measuring tasks. The time measurement at the target object is achieved by modulating the laser beam. The accuracy of the distance measurement on the other hand is determined mainly by the uniformity of the rotational speed. In the case of a deviation of the actually travelled angle of, for example, 100 μrad from the setpoint value over an angle of rotation of 45 degrees, a relative distance error of only 400 μrad/π=127 ppm is produced. In the case of distances of up to 50 m to be measured, errors of 6.4 mm therefore occur, which is too inaccurate, for example, for tasks in the construction sector.
A system comprising a cycling distance measurement for a mobile working machine is described in the International PCT application with the application number NO. PCT/EP2007/007058. There, a position determination apparatus has a transmitter for the emission of optical emitted beams, a receiver and a deflection means rotatable about a vertical axis for guiding the transmitted beams in horizontal directions. The deflection means define a plane which is substantially horizontal and in which the received beams are also detected by the receiver. After their emission and subsequent reflection by the reference objects, the transmitted beams are detected again by means of a receiver of the positioning system, the distances to the reference objects being determined from the received signals of the receiver, in particular according to the phase measurement principle or the principle of pulse transit time measurement. The directing of the transmitted beams towards the reference objects and of the reflected beams as received beams towards the receiver are effected by the deflection means. However, the measurement in this plane is effected from the movement and to a few, typically four, cooperative targets, i.e. reflectors, which are placed at known positions. By means of these measurements, the position of the measuring unit relative to these cooperative targets is determined so that, from a knowledge of the position thereof, it is possible to derive that of the moving unit. The rangefinder described there is neither intended nor suitable for determining points on noncooperative surfaces. Since it operates according to the conventional phase measurement principle, it is too slow for the angular speeds required in the projection of a reference line. At the high speeds required for this purpose, the laser would experience a blurring of the measurement during a measurement to the target object. In addition, the device requires a large amount of space since, in the case of the biaxial arrangement of transmitter and receiver described, the latter rotates around the transmitter. Finally, there is no projection of marks which can be detected by the eye or detectors and permit guidance of the user or referencing by a further surveying unit.
EP 1 001 251 discloses a laser scanner having a distance-measuring and target-tracking function, which comprises a device for producing a visible laser beam and a transmission optical system having controllable deflection means rotatable about two nonparallel axes. The deflection means are actuated with point resolution by means of servo motors and angle encoders according to a specified arbitrary pattern. As a result, firstly a projection of arbitrary point, line or area patterns onto, for example, a room wall and secondly exact surveying of the room and beam tracking relative to moving objects are permitted. However, there is no automated and continuous measurement of points in the path of the projected pattern. Moreover, the scanning measurement of points means that a complete determination of the distance with the desired or required accuracy must take place in each of these measurements during only a single pass through the scanning path. If the environmental conditions are too poor, aids must be used or a measurement cannot take place. The measurement to weakly back-scattering surfaces or to objects which are temporarily concealed is therefore not possible. However, the latter point is of importance particularly in the construction sector when, for example, a device projecting a reference line is operated in a room and the user continuously interrupts the moving beam with his body, so that a single survey gives only incomplete results.
U.S. Pat. No. 5,629,756 describes a rotary laser by means of which, with the use of a special reflector element on the wall, the distance to the wall can be measured. This distance is used in order to focus the laser line onto the wall so that a clearly recognizable, sharp line is produced on the wall. In addition, it is proposed to use the measured distance for adaptation of the rotational speed since—in the case of a distance to the wall of, for example, more than 30 m—the projected laser line is thus better detectable at lower rotational speeds. Moreover, this solution is not capable of measurement to natural surfaces, i.e. even without use of a reflector, under all conditions prevailing in normal operation.